Method and apparatus for measuring fat content in animal tissue either in vivo or in slaughtered and prepared form

ABSTRACT

A method is presented and apparatus disclosed which permits very accurate measurement of the fat-to-lean ratio of meat, whether in vivo or in prepared form. The animal or meat package to be analyzed is subjected to a varying electromagnetic field generated by applying a radio frequency signal to a solenoidal coil through which the sample passes longitudinally. Because of difference of electroconductivity and dielectric properties between various body components, the load observed by the source which drives the solenoidal coil takes on a different value from that of the empty sample zone. By utilizing other predetermined parameters of the sample, the load difference may be utilized to infer the fat-to-lean ratio to a commercially acceptable standard.

United States Patent Barker 1451 May 22, 1973 [54] METHOD AND APPARATUSFOR 3,080,507 3/1963 Wickerham et a1 .324 34 R MEASURING FAT CONTENT 13,224,320 10/1965 Knudsen ..17 1 R ANIMAL TISSUE EITHER IN VIVO OR OTHERPUBLICATIONS IN SLAUGHTERED AND PREPARED FORM Winters, S. R.; ElectronicEgg Grader; Radio-Craft;

Sept. 1947, pp. 22 and 61 [75] Inventor: Wesley H. Harker, ParadiseValley,

Ariz- Primary ExaminerRobert J. Corcoran [73] Assignee; The Emme CompanyGlendale Altorney William C. Cahill, Samuel J. Sutton, Jr.

Aria and Edwm M. Thomas et al.

22 Filed: Oct. 4, 1971 ABSTRACT 2 App] 1 05 A method is presented andapparatus disclosed which permits very accurate measurement of thefat-to-lean ratio of meat, whether in vivo or in prepared form. U-S- R,R, R, The or meat package to be analyzed is ub- 128/2 R jected to avarying electromagnetic field generated by Int. Cl. ..G01l' a radiofrequency signal to a solenoidal coil [58] Field Of Search ..324/34 R,40; thr u h which the sample passes longitudinally. 1 l 128/2 2 Becauseof difference of electroconductivity and Z dielectric properties betweenvarious body components, the load observed by the source which drives[56] References Cited the solenoidal coil takes on a different valuefrom that of the empty sample zone. By utilizing other predeter- UNITEDSTATES PATENTS mined parameters of the sample, the load difference2,362,774 11 1944 Romanoff ..324 40 may be utilized to infer thefat-046311 ratio to a 2,667,159 1/1954 Goldberg et a1.. .l28/2.05 vmcrcially acceptable standard. 2,763,935 9/1956 Whaley et al l28/2.l R

11 Claims, 8 Drawing Figures CALIBRATE SAMPLE 3/) 30) 29? 45f ZELZ; g

| DIRECT DRIVE RECTIFIER I REFERENCE COMPARATOR SMOOTHER 1 ZE L J 21 i22 23 25 O VARIABLE IMPED. 34 9 WAVEFOR GA|N BUFFER CONDITIONER r SOURCESTAGE AMPL- AND FILTER E COIL 39 3a; 37 36 352 VOLTAGE SENSE SUBSYSTEMDISPLAY 0R ZERO AND 1 SIGNAL CD OggiiuliQAgA INTEGRATE EDAJIIIJGSEFCONDIT'ONER DETECTOR g CURRENT z iINTEeR. A SENSE RECORD 40 ON/OFF l 4/TIMING z jggggl com oL SIGNAL {CALIBRATE LOAD posl noN 1 I A l ADJUST lA sENsoR 1 L ff i fii i B E 52 Q L EE? J T L 44- MEASURE INITIATE r 42 LI MEASURE INITIATE MANUAL I CIRCUIT I MEASURE BUTTON Patented May 22,1973 5 Sheets-Sheet 1 IE-l ICE-3 N I 2 Q LEAN NIQQ NIO NIE OO 66 OHM-MFAT 3.3 OHM-M NIE O LOG [0 OF FREQUENCY LOG IO OF FREQUENCY TYPICALBEHAVIOR OF RESISTIVITY TYPICAL BEHAVIOR OF DI ETECTRIC CONSTANTINVENTOR.

WESLEY H. HARKER IlE-E BY fiMQ/z ZAW M ATTORNEYS Patented May 22, 19733,735,247

5 Sheets-Sheet 2 DRIVE POWER OSCILLATOR AMPLIFIER SENSE COIL ANDFEEDBACK SENSOR ELECTRONICS I II LE- 5 WEIGHT lNPUT- DATA QUTPUTINVENTOR. DIMENSION INPUT BE EY H HARKER ATTORNEYS Patented May 22, 19735 Sheets-Sheet 5 A PQB Q3 Nov-lama:

INVENTOR.

WESLEY H. HARKER BY KMQ MV wc'w ATTORNEYS METHOD AND APPARATUS FORMEASURING FAT CONTENT IN ANIMAL TISSUE EITHER IN VIVO OR IN SLAUGHTEREDAND PREPARED FORM This invention relates to the measurement arts and,more particularly, to method and apparatus for determining thefat-to-lean ratio of meat.

Recent studies in the field of health and more have lead to an increasein the value of lean meat over fat. Thus, the value of an animal to ameat processor is very closely related to the percentage of lean meatcontained in the animal. The processor has had no truly reliable rapidmethod to determine the lean weight in animals offered for sale to himand usually relies simply upon human judgment. Similarly, the breeder ofanimals has been forced to slaughter a part of each generation in orderto determine their meat quality. However, because lean characteristicshave a heritability of only approximately 45 per cent, the siblings ofthe slaughtered animal often do not possess the analyzed quality. As aresult, a time span of perhaps five years may pass before a breederbecomes fully aware that an inadequate animal has been chosen as a sire.

It will therefore be appreciated by those skilled in the art thatapparatus capable of accurately indicating fatto-lean ratio of a sample,including a living animal, without physical contact and in a completelynondestructive manner would be highly desirable, and the method andapparatus of the present invention are directed to this end.

It is therefore a broad object of the present invention to providemethod and apparatus for accurately measuring the average percentage offat in a sample of animal tissue.

It is another object of this invention to provide apparatus foraccurately measuring the fat-to-lean ratio of a living animal withoutphysical contact and in a nondestructive manner.

A further object of this invention is to provide animal breeders withaccurate means for selecting animals to retain for breeding purposes.

Yet another object of this invention is to provide meat processors withmeans for determining the quality of an animal prior to its purchase.

Contemporary emphasis in animal nutrition is directed toward providingmaximum weight gain because no adequate means exists to inexpensivelyand rapidly determine the lean content of a growing live animal. Thoseskilled in the art appreciate that an optimum feed regime would bedirected toward maximizing lean weight gain.

It is thus yet another object of this invention to provide animal,including human, nutritionists with means to optimize the lean weightgain rather than the gross weight gain in accordance with specificdiets.

Yet another object of this invention is to provide researchers in animalscience and human nutrition to measure body fat in living specimens on aroutine basis.

Yet a further object of this invention is to permit such routinemeasurements without immobilization or anesthetization of the subject.

Still another object of this invention is to provide method andapparatus for measuring meat during and after the processing cycle topermit accurate mixing to a predetermined fat content and to determinethe meat quality and value.

The manner in which these objects are achieved will be understoodthrough a consideration of the following specification and the drawingof which:

FIG. 1 is a schematic diagram of a shielded solenoidal coil driven by atime varying current source depicted with a sample to be analyzeddisposed within the elec tromagnetic shield;

FIG. 2 is a graph illustrating the relative conductivities of fat andlean meat as a function of frequency;

FIG. 3 is a graph illustrating the range of dielectric constants of leanand fat meat with respect to frequency;

FIG. 4 is a partially cut away representation of an idealized form ofthe field generating subsystem of the present invention;

FIG. 5 is a graph illustrating three functions of importance inunderstanding the present invention with respect to a parameter relatedto the electromagnetic characteristics of the apparatus constituting thepresent invention;

FIG. 6 is a major block diagram illustrating broadly the manner in whichthe method and apparatus of the present invention may be practiced;

FIG. 7 is an exemplary nomogram presented as one method of reducing ameasurement made by the apparatus to a value directly related to meatquality; and

FIG. 8 is detailed diagram illustrating the electronic andelectromagnetics of a presently preferred embodiment of the inventionincluding certain options and alternatives which had been found usefulfor specific applications.

Briefly, in accordance with a presently preferred embodiment of theinvention, the animal or meat volume is placed inside along the axis ofa long electrically conducting coil. The coil is shielded by goodelectrically conductive material to guard against extraneous influences,and the shield is open at both ends to allow entrance and egress of theanimal or sample. For accurate operation in measuring whole sample fat,the coil extends well beyond the ends of the sample and the shieldbeyond the ends of the coil. The fundamental measurement techniqueconsists in measuring either the change in resistance or the change intotal impedance between the empty and occupied coil as seen by thesource driving the coil. This change, expressed in a suitable form suchas ohms, phase angle, complex admittance or other forms known to thoseskilled in the art, is then used, in conjunction with the weight, tocalculate the amount of fat in the sample. Predetermination ofadditional parameters, such as the width of the sample, can be used toimprove the accuracy of the measurement, although highly satisfactoryresults are routinely obtained from knowing simply the weight andspecies of a living animal. The calculation may be carried out by handusing appropriate mathematical formulas, with a prepared nomograph, byusing a set of specially prepared tables, or by incorporatingappropriate analogue or digital computing circuits in the apparatusitself.

The measurement action is based on the differing electrical propertiesof lean and fat animal tissue. The conductivity of lean tissue, thanviscera and, in vivo, the skeleton is much higher than that of the fattytissues. Over frequencies ranging from kiloHertz to 10 gigallertz, thisratio will typically be between 5 and 100. A second electrical propertyof interest is the relative dielectric constant. Over the abovefrequency range the ratio of lean to fat dielectric constants wilttypically lie between 1.1 and 10.

By creating time varying electric and magnetic fields in the sample,currents are induced in the sample. These currents cause power lossesand phase shifts that are reflected back into the field source asresistive and reactive changes caused by the samples presence. Dependingon the configuration of the driving fields and the sample size andweight, the changes are interpreted in terms of lean content. If thesample is not a live animal then the approximate temperature of the meatmay also be required for an accurate reading.

More specifically, the majority of body cells contain electrolyte whilefat does not. Thus, fat has a much lower electrical conductivity thanlean meat. For example, at a frequency of 10 megaHertz, lean conductsapproximately twenty times as well as fat. Similarly, the dielectricconstants differ, fat having around one-tenth that of lean. Theconductivities and dielectric constants both vary with frequency, but ithas been found that the ratios between the values for fat and lean stayrelatively constant. Presently, available experimental evidence israther sparse, but apparently, as previously noted, the bone and viscerahave conductivities, in vivo, near that of lean. Thus, a measurement ofwhole body conductivity is closely equivalent to determining thefraction of body fat.

The average electrical conductivity of the sample on a homogeneousvolumetric basis is:

o'=fcr,+ (l f) Similarly, the average relative dielectric constant is:

in the above formulas, ois electrical conductivity in mhos per meter, 6is the relative dielectric constant and f is the fraction of fat. Thesubscripts f and 1 stand for fat and lean, respectively. These equationsare not exact because of the effect of boundaries and otherheterogeneities within meat. They are qualitatively correct, however,and serve to guide interpretation of experiments.

From the foregoing, those skilled in the art will understand that themeasurement of the average conductivity or dielectric constant wouldlead to the determination of f, the fat fraction. Detailed correctionsfor heterogeneous and other second order effects can be determinedeither on an empirical basis or by applying detailed theoreticalconsiderations. Several methods for measuring the approximate averageelectric constants have been considered and each is useful over somerange of sample and application type. Before a detailed description ofthe presently preferred embodiment of the invention is presented, thefollowing discussion will serve to sharpen the differences between thealternatives, some of which have been considered in the prior art.

Capacitive or direct coupling is the classical approach to themeasurement of dielectric constant. Generally, such measurements arecarried out with a carefully controlled sample geometry. The driveelectrodes are either in direct contact with the sample or separatedfrom it by a small insulating layer. For accurate measurements of groundmeat samples, this is a useful approach. The method is, however, verysensitive to small dimensional variations and included boundaries withinthe sample. In live animal measurements, problems arise from thevariation of shunt capacitance from animal to animal. The designs tocorrect these problems'deposit'o'nly a tiny fraction of the field energywithin the animal resulting in a small signal in high backgroundmeasurement problem. Direct contact has the additional problems ofsecuring a uniform current density within the sample as well as contactpotential and (animal) skin effects.

Radiative coupling is that in which the sample interacts with anelectromagnetic radiation field from source within a controlledenclosure. Such an interaction affects the loading of the source and isthus susceptible of interpretation in terms of the samples physicalcharacteristics. Again this technique is effective for small, controlledgeometry samples. In general, the need for high radio frequencies togenerate a good signal leads to problems. First, a thick sample absorbsall the radiation in the surface layers leaving the interior unmeasured.Second, large samples have dimensions equivalent to many wavelengthsresulting in high sample position sensitivity.

Inductive coupling deals with then near field of source. The testgeometries can best be described in terms of the induced magnetic field.A solenoid coil (or a pair of Helmholtz coils or other conductorconfiguration) carries a time varying electric current. The currentcreates a region of time varying magnetic flux. Any object within thisregion will have an electric field induced in it which in turn causespower to be dissipated if a finite conductivity is present. Theinductive coupling method is convenient because of the ease ofconstructing large test regions and the relative insensitivity to otherperturbing factors such as the air gap between the sample and the drivecoil. The field, however, must be carefully shielded to minimizeextraneous influences, and the drive coil must be relatively longcompared with the sample to provide a spatially uniform sampling field.The induced sampling voltage in the most natural configuration, thesolenoid coil, increases with sample radius requiring carefulinterpretation. The inductive field approach, in the broad sense, offersthe most convenient live animal technique.

As mentioned in the foregoing, drive coils can take many configurationsdepending upon the application. For high rate, live animal or meatsample measurements, the axial solenoid coil has been determined to bean excellent configuration. It is easily shielded and driven, and byproper design a reasonably large axial uniform field zone can begenerated. All the important field configurations for the axial solenoidcoil can be resolved into two components, the transverse magneticcomponent with electric field lines parallel to the axis (TM) and thetransverse electric component with the magnetic field lines parallel tothe axis (TE). The TM mode has a considerable advantage in that theelectric field remains constant with changing radius. This permits easyinterpretation of the readings and reduces the effect of radial sampleanomalies. Unfortunately, at the frequencies of interest, solenoid coilsof the requisite dimensions function as wave guides operating belowcutoff. As a consequence, it is very difficult to generate a uniform TMmode. Large drive currents must be applied and great care must be takento maintain uniform coil conductor thickness.

Thus, while other approaches are possible, the TE mode for the animalmeasurement instrument constitutes the presently preferred method andapparatus of the invention. The TE mode is generated by driving a spiralcoil wound in a solenoidal configuration. Although a practicalembodiment may differ from a simple constant radius solenoid with auniform spiral winding, all of the basic principles involved in theinvention can be understood through its analysis.

Consider the uniform constant radius spiral solenoidal coil 1 beingdriven by a sinusoidal current generator 2. The coil 1 is surrounded bya good electrical shield 3 on the outside to prevent interference withthe measurement and to minimize radiation. A cylindrical test sample 4is introduced within the coil. Maxwells equations can then be solvedthroughout the system and the effect of the sample 4 on the load currentpredicted. The general solution is quite complicated mathematically. Forthe frequencies of interest, however, a very good approximation can bereached by neglecting the effect of the currents induced in the sampleon the shape of the drive field. This is the so-called quasistaticapproximation.

Within the test volume a spatially uniform magnetic induction B iscreated with force lines parallel to the axis:

B B e Where:

B is the time varying induction, B is the induction amplitude, to 21wthe angular driving frequency, j square root of l. Throughout the volumecontaining B, a coexisting electric field is created:

Where: r is the radial distance from the axis. The power induced in auniform homogeneous sample is:

R P=21rf crE rdr O (17/8) B 0'w RL (1r/8) B 00 (W/p) R Where:

R is the sample radius,

L the sample length,

W the sample weight,

p the sample density. Equation (1) is a good approximation to theinfluence of each variable on the real part of the load impedance. Ifthe change in the reactive component is desired, the analysis must beextended to include the effects of the currents induced in the sample. Arough calculation shows:

Resistance/Reactance 1/6 p 01013 Where: 1. is the permeability of freespace. Because equation (I) is valid only when amR is small the changein reactance is second order to that in resistance.

Possible measurement variables can be inferred from the abovediscussion. Measurement of power, resistance, reactance, phase angle orresonance frequency change with sample introduction all serve to deducethe conductivity and, as a result, the fat fraction from equations (1)or (2). Multiple frequencies and pulsed drive techniques also suggestthemselves. In the presently preferred apparatus, a combination of powerand phase measurement techniques is used because of engineering andeconomic considerations although this choice is not basic to the heartof the invention.

In the engineering, manufacturing, and use of the apparatus, severalconflicting requirements are placed on he available design variables.These constraints, once recognized, give limited ranges for optimumoperation as well as introducing other considerations into the design.For example, from equation (1), it will be apparent that the power risesas the square of the frequency due to the increase of induced electricfield. In addition, the conductivity may also increase. Thus, thesensitivity increases with increasing frequency. A more thoroughanalysis shows, however, that a better approximation to the behaviorgives power as proportional to the real part of:

1 /1 1 (P U/[ o (P Where: J and J are Bessel Functions,

p k e jp mo',

k w/c, c,

c is the velocity of light.

For reasonably small values of the argument, the above formula predictsthe power rising with the square of frequency. As frequency continues toincrease, however, the power will go through a succession of maxima andminima. Also the power will be more and more concentrated in the surfacelayers so that the internal composition will have little influence onthe reading. The balance to be made for whole body reading is betweensignal strength, requiring high frequency, and good averaging of thesampled volume, requiring low frequency. A second practicalconsideration is the difficulty of balancing current distribution inlarge systems at high frequencies.

A useful range is set by the parameter [L GJO'b when the displacementcurrent term is small. This parameter is about twice the square of theratio of sample radius to skin depth. For reasonable power withoutserious self shielding, the parameter can range from perhaps 0.01 toabout 35. At the upper limit, the self shielding is about 50 percent.Operation at higher frequencies can be used to deliberately focus on theouter regions or, by differencing, on the inner regions. By way ofexample, a hog-sized machine according to a presently preferredembodiment, operates at 5Ml-Iz, and a smaller machine for analyzing-pound boxes of beef operates at lOMHz.

Equation (1) can be rewritten displaying the dependence of power onsample geometry as RL. The fourth power of sample radius arises becauseboth the amount of material to conduct electricity and the amount ofmagnetic flux coupled both increase as the square of the sample radius.The typical sample in actual practice is not a perfect section of aright circular cylinder. Hence, two external sample shape effectsinfluence the reading; viz.: the coupling to the field and thenoncylindrical shape of the sample. Of course, for a fixed sample shapesuch as a box, these factors are constant and can be calibrated out.

However, for the measurement of live animals, even though there isconsiderable individual variation, the general topology is the same.This problem has been studied in terms of idealized solids, and it hasbeen determined that a fairly general heuristic form can be used toapproximate the effect. If the ratio of the shape corrected power to theperfect cylindrical power is written as S, then a reasonableapproximation to S will have the form:

Where:

C, and C are general constants,

w is maximum body width,

d is maximum body depth.

Although C and C, can be analytically estimated, in practice it is moresatisfactory to determine them experimentally. it will be noted that themeasurement of the width w, the depth d, and the length L are requiredfor the use of this correction. For high speed, slightly lower accuracyfat-to-lean measurements, these factors in turn can be adequatelyestimated from a knowledge of the animals species and weight.

Although the shape correction factors are basically concerned withvolume, as is the basic measurement itself, it is usually practical toonly measure the weight. The volume, V, is related to the weight as:

The density of fat will range a few percent below 1.0 and that of lean afew percent above. Writing 0'; and 0', for the densities of fat andlean, respectively:

The difference between the two densities is small and can be ignored formost of the measurements contemplated.

ln the foregoing discussion, the tacit assumption has been made that thesample is homogeneous; i.e., the fat and lean being uniformlydistributed. in a real animal this is by no means the case. While, ingeneral, the topological distribution is the same from animal to animal,there are variations due both to congenital and environmental factors aswell as those due 0 differences in fat volume. The most significantmanifestation of the latter is in the outer body far covering. Thiscovering is also at the most sensitive radial point to influence thereading.

A suitable approximation has been found by treating the animal as twoconcentric cylinders, the outer one of almost pure fat and the inner onecomposed of lean with some fat mixed in. The ratio of power with aheterogeneous configuration to that of a homogeneous configuration, I,has the from:

y the fraction of body fat found in the lean central region.

placed in more convenient form:

The conductivity and dielectric properties of matter are usually afunction of temperature. In the live animal this is not series becausethe homeostasis of mammals keeps the temperature within a narrow rangefor each individual, and the variations between individuals of a breedor species are minimal. For fresh, prepared meat measurement, thetemperature may have to be separately determined. For example, in beef,the correction is around 0.75 percent fat per degree Fahrenheit.

Additional sources of variation in the conductivities and dielectricproperties are the congenital and environmental effects mentioned above,the effects of different feed regimes, the animals emotional state, etc.No serious errors have been observed from these supplementary factors.

In measuring live animals certain additional factors must be considered.Measurement rate may be traded off against measurement accuracy. Forhigh accuracy, the animal may be stopped momentarily with doors or otherbarriers. He may even be totally immobilized with drugs. To measure theanimal in motion passing through the machine at his normal gait, whichthe apparatus disclosed below is capable of doing, the detailed outputversus time may be recorded for later interpretation. Alternatively, aposition sensing system may be used to initiate a single reading, or theoutput may be integrated over a given length of time or over a givenlength of the instrument.

There are three prime sources of measurement variation with the liveanimal: the bunching and unbunching of muscle groups during motion, thebreathing, and the time variation of the average radial moment of theblood volume. In order to provide sufficient integration to average outsome of these effects, the animal must either be halted or the tube mustbe relatively long. For example, for hogs, an eight foot tube with a 0.5second integration time gives good results on moving animals as will beexplained in further detail below.

In the foregoing discussion, some of the factors influencing the outputof the device have been outlined and an indication of the approachdeveloped to control or correct for each factor given. In the following,the approaches used to obtain practical results in a specific reductionto practice are discussed. To briefly summarize, the animal is placed ina time varying electromagnetic field. The field induces electricalcurrents within the animal. The phase and magnitude of these currentsrelative to the drive field are determined mostly by the gross effectivelean meat mass of the subject. Other ef fects, however, modify theapparent circuit load due to the animal. Among these are internalstructure, external body geometry and muscle and blood pool motion.Precise measurement requires immobilization of the animal plus detailedmeasurements of body dimensions including perhaps the thickness of theouter fat layer. Both analysis and experimental results show, however,that standard errors well within present practice can be obtained bymeasuring animal weight and its loading effect on the circuit only. Theremaining measurements can be used to extend the accuracy well beyondthat achieved by the disclosed apparatus for those applications in whichsuch precision is required.

Collecting the results of the above equations together into one basicequation gives:

V is the perfect cylindrical volume,

8 is the density sensitivity ratio (p, pf)/pf Equation (6) is the lowfrequency approximate design equation for the system. If appropriatevalues for the variables are known, the predictions it makes areaccurate within a few tenths of a percent.

In cases where less accurate measurements are required and where a highmeasurement rate is needed, the several parameters such as V and 'y canbe estimated in a different manner.

First, equation (6) is reduced to a form almost as accurate, but moremanageable. 1 7 is effectively measured by the thickness of the outercovering layer. Approximately:

Using this, the heterogeneity bracket in (6) has the form:

A second practical problem in the utilization of equation (6) is toestimate the perfect cylindrical volume, V from the animals weight.Experience has shown that an equation of the form gives relativelyaccurate results. Thus, incorporating all of these considerations intoequation (6), a practical accurate form of the basic equation is:

E C.,R W(l Cm (1 CGT/R) where E is the EMME number, and

C C C are species dependent constants, and because these C" constantsare affected by such factors as dressing practice or chemical analysistechnique embedded in their values, they are best determined empiricallyby close inspection of slaughtered animals which have been analyzed bythe apparatus.

For higher measurement rate it is possible to reduce the accuracysomewhat and estimate T and R from the weight and the EMME reading only.With respect to T, the fat covering thickness, the ratio ofT to thetotal radius R can be deemed to be linearly related to the fatfraction,f. R, in turn, is related to the cube root of the total volumeor the weight. These considerations lead to the following equationinvolving only E, W and f.

(8) gives f in implicit relationship to E and W. The last step is toapproximately invert this relation.

Equation (9) has been applied to the high rate measurement of marketweight hogs. On single animals it predicts lean cut weight with acorrelation coefficient of around 0.9. Used on a multiple animal batchbasis, batch accuracies of better than one percent are achieved.

It also will be apparent to those skilled in the art that a machinewhich automatically determines the dimensions by photoelectric or othermeans, the backfat by ultrasonic or other means and/or the weight byload cells or other means can be incorporated into the apparatus toprocess animals both at high rate and high accuracy.

As previously noted, the behavior of resistance in both the fat and leanpotions of meat varies with frequency. Over frequencies ranging fromkiloI-Iertz to 10 gigaI-Iertz, the ratio between fat and lean willtypically be between 5 and 100. FIG. 2 is a graph depicting theresistivity/frequency characteristics of the frequency range ofinterest. Similarly, as also noted above, the relative dielectricconstants oflean and fat also vary with frequencies, and FIG. 3illustrates empirically determined values in the frequency range ofinterest.

The somewhat idealized configuration of the measuring apparatus shown inFIG. 4 may be analyzed to provide a formula which has proved accurate inpractice. The coil 5 is taken to be solenoidal in nature so that theinterior magnetic field lines are dominantly parallel to the coils axis.The impedance reflected into coil 5 by a homogeneous sample 6 isapproximately proportional to:

driving source for A l is shown in FIG. 5. Inspection of FIG. 5demonstrates that a rather limited range of the parameter p msgivesuseful sensitivity. Note that this parameter is proportional to thesquare of the ratio of sample radius to sample skin depth. A secondfactor limiting useful frequency range is, of course, the self shieldingof the sample at high frequencies. The curve labeled Average-to-PeakPower is indicative of the extent of this effect. It should be pointedout that, if only the surface regions of the sample are of interest, thehigher frequency ranges can be used effectively. For example, consider amachine according to FIG. 4 which is intended to measure live swine. Atypical coil cross-section would be on the order of 16 by 24 inches toaccommodate animals ranging up to 350 pounds. For these conditions, aswill be evident from FIG. 5, a frequency between 1 and 20 megal-Iertzmay be selected to give useful results.

terial composition may be resolved. Pulsing or other,

time modulation techniques may be used to accomplish the same purpose.

FIG. 6 is a major block diagram of the electronics utilized in typicalembodiment of the invention. The drive oscillator 11 provides aprecisely controlled frequency voltage signal to a power amplifier 12.The power amplifier 12 uses this signal to produce a precisely controlled drive current to the coil system (FIG. 4). A feedback sense coil13, positioned in or near the sample volume, provides a feedback signalto the power amplifier 12 so that the amplifier maintains a constantdrive current. Sampling the voltage across the coil system and comparingit to a reference signal from the power amplifier 12, a phase sensor 14develops a signal proportional to the effect of the sample within thecoil 5 compared to an unoccupied condition. Inputs for sample weight andsample transverse dimension are provided to data reduction subsystem 15along with the signal from the phase sensor. The data reductionsubsystem then computes and displays the approximate lean weight and/orlean percent. It may be noted that, in the case of transverse magneticdrive with a coaxial cylinder rather than a coil, the transversedimension input may be omitted for equivalent accuracy.

Depending on the form of the sample, i.e. live animals, carcass parts orprocessed meat, different handling and positioning mechanisms areprovided to expedite sample flow.

Referring again to FIG. 4, a typical machine can be reviewed. The liveanimal or package of meat products are introduced into measuring volume9. For animal use the measuring volume is usually a straight throughtube open at both ends. Sampling magnetic and electric fields areinduced into the volume 9 by the transducer coil 5 which is wound orotherwise applied to a supporting structure 10. The coil 5 iselectromagnetically excited by the drive chain illustrated in FIG. 6.Problems of mode shifting and impedance bypassing are.

corrected by directly sensing the magnetic field in the coil systems 5sample space 9 or in the exterior region 16 between the coil structure 5and an electromagnetic shield 17 by means of the feedback sense coil 13.This feedback signal is impressed on a variable gain or equivalentcontrol element coupled to the power amplifier 12 to maintain constantsense fields current into the coil. Of course, other indicators ofconditions in the sample volume may be used instead of direct fieldsensmg.

The electromagnetic fields in the sensing volume 9 are time varying.They therefore induce currents within any sample 6 within the samplingvolume 9. The magnitude of these currents is roughly proportional to theapplied drive current, the coil 5 turns per unit distance, the localcross-sectional area of the sample 6 (in the case of transverse electricdrive), and the local conductivity of the sample 6. The local dielectricconstant influences this induced current to some extent, but forillustrative purposes may be neglected. The induced currents causeenergy loss in the form of Joule heating. This loss, in addition to theelectrical inertia effect of the induced currents, is reflected backinto the coil system 5 as a change in complex electric impedance. Thisimpedance change or, equivalently, energy loss, is

sensed by the sensor elecronics 14. Through the use of formula (1), anomogram such as FIG. 7, the graph of FIG. 5 or equivalent analytical orgraphic means, the parameter n t-r05 may be found. By factoring in theanimals or samples weight and, if desired and practical, its dimensionsthe quantity 0, the conductivity is closely determined from whichpercent lean is the given as 1 10007 iao/( lean rm) As noted above, theuse of nomograms or appropriately designed or programmed computers canaid the computation process. Hence, the data output 15 may take manyforms from a meter giving an unanalyzed quality number to a completelyanalyzed data output stream.

FIG. 8 presents a more detailed functional block diagram of a presentlypreferred implementation of the invention and also includes certainalternatives and optional elements for completeness in the followingdiscussion. Two major systems are included in the electronics, viz.: thedrive system which functions to excite the sensor volume within the coilsubsystem 27, and the sense, interpret, and control system whichfunctions to sequence, analyze, and display the results of themeasurement.

The drive system commences with a waveform source 21 which is typicallya single frequency oscillator although, for more versatile applications,it may issue, selectively, multiple frequencies or may provide morecomplex repetitive waveforms such as square waves. The signal issuingfrom the waveform source 21 passes through a variable gain stage 22which has the purpose .to maintain a constant drive output for thereasons previously discussed and described further below. The gaincontrolled signal is then amplified by a buffer amplifier 23 to raisethe signal amplitude to a level sufficient to drive a power amplifier24. The power handling capacity of the power amplifier 24 may range fromabout 0.1 watt to watts depending upon the application contemplated andthe size of the sensor volume.

The impedance conditioner and filter 25 may optionally be incorporatedinto the apparatus to permit tuning the coil subsystem 27 to or close toresonance in order that maximum current delivery may be achieved withoutunduely high voltage. Additionally, filter elements may be incorporatedto remove any waveform distortion observed to have been introduced inthe drive chain.

A sensing and feedback subsystem is utilized to maintain a constantdrive to the coil subsystem 27, and two alternative sensing methods arepresented in FIG. 8. The parameter best held constant is the magneticfield strength within the sensing volume. Recognizing that the magneticfield strength is, to a first approximation, proportional to the drivecurrent, the drive current can be sensed with current transformer 28 orthe like. The alternative, previously discussed in conjunction with FIG.6, is the utilization of a direct pickup coil 32 within the shield orcoil volume. Utilizing either type of sensor, the output signaltherefrom is fed to a rectifier/- smoother stage 29 which converts thedetected signal to a slowly varying d-c signal which is proportional tothe magnetic field amplitude. The signal issuing from therectifier/smoother 29 is impressed as one input to a voltage comparator30 which also receives an input from a previously calibrated drivereference source 31. The voltage comparator 30 continually compares thetwo input signals and, if the two differ in amplitude, functions toadjust the variable gain stage 22 in the appropriate direction to bringthe amplitudes into correspondence.

In practical embodiments of the invention now being considered, the coildrive signal may usefully be fed into a coil drive distributionsubsystem 26. Because the total length of the coil winding in the coilsubsystem 27 may be several wavelengths long, a simple two connectionfeed system, as depicted in FIG. 6, may be impractical. The coil drivedistribution subsystem 26 drives the coil subsystem 27 as severalparallel coils or as a compound coil with several interlaced windings.The coil subsystem 27, which is contained within a suitableelectromagnetic shield not shown in FIG. 8, converts the electriccurrent from the drive chain into a time dependent electromagnetic fieldthroughout the volume within the shield. As previously discussed, thisinduced field sets up electric currents within any conductive sample inthe shielded volume, and the effects of these currents are reflectedback to the drive chain where they may be interpreted as changes inreactance in the coil subsystem 27.

The primary function of the sense, interpret, and control system is tomeasure and interpret the changes in the impedance of the coil subsystem27 brought about by the introduction of a sample into theelectromagnetic field. Additional functions, such as the initiation,sequencing, and performance of calibration and correction adjustments tothe apparatus may be incorporated.

The drive current to the coil subsystem 27 and the voltage impressedthereon are sensed, respectively, by current and voltage sensors 34 and33. The signals sensed thereby are impressed upon the input terminals ofa detector stage 35 which issues a d-c voltage signal which isproportional to the phase shift induced by the sample as well as theintroduction of the change in impedance magnitude. Those skilled in theart will readily appreciate that alternative functions of the stagerepresented by the detector 35 might deliver signals proportional tochange in power, change in real impedance, etc., which signals can beanalyzed to extract the desired information. The signal issuing from thedetector 35 is usually low level such that an amplification and signalconditioning stage 36 is useful. In order to ease circuit designproblems in the succeeding stages, the stage 36 may advantageouslyincorporate a chopper to convert the d-c signal to a corresponding a-csignal.

In order to permit ready adjustment for system parameter changes, azero-and-range adjust stage 37 may be provided, and may simply take theform of manually adjustable potentiometers. Thus, the zero output is setwhen the test volume is unoccupied, and a standard calibrated sample 45is then placed in the test volume to permit making the range setadjustment. This procedure insures that all tested samples are referenceto a standard for the measurement of their lean content. For thoseapplications in which the environment in which the apparatus is utilizedis expected to vary widely, automatic zero adjusting is desirable tomitigate the effects of drift. The stage 37 then includes a zeroseekingservo loop to adjust out any such drift. However, to prevent thiscircuit from altering the reading during a sample measurement, anoccupied sensing circuit 41, which may be a simple photoelectricdetector or the like, is used to determine that the test volume isoccupied and therefore disables the automatic zero adjust function.

Similarly, an automatic range adjust may be usefully incorporated intothe element 37. For this purpose, a timing and control circuit 40institutes activity which causes a fixed calibrated load 46 to beinserted into the sensing volume at predetermined intervals. Theoccupied circuit 41, again, may be utilized to suppress thisself-calibration function when the sensing volume is occupied by asample being measured. The timing and control circuit 40, wheninstituting the range calibrated function, locks the zero adjust servoloop in the element 37 and enables a range servo loop therein whichadjusts the range fed until a standard level output is achieved afterwhich the automatic zero adjust mode is reenabled. Theseself-calibrating techniques are very well known to those skilled in theanalogue computer arts.

The measurement signal issuing from the adjustment stage 37 may beimpressed directly on an output stage 39 or first passed through anintegrator 38. It has been determined that, in the case of livespecimens where both body and blood volume movements induceperturbations in the measurements, it is helpful to integrate the signalover a period of time to provide a partial averaging effect. As apractical matter, the integration may be initiated by an operatorspressing a measure pushbutton 42 when he observes that the subject is inposition. This causes the timing and control circuit 40 to activate theintegrator 38 for a predetermined phase length of time which may range,for example, between 0.1 and 1.0 seconds for hogs. After the integratorhas been deactivated, a record signal is issued to the display and datacapture system 39 which holds the value for display on a meter, forprinting, for recording on magnetic or paper tape, or otherstraightforward means for capturing the data. For example, the meter maybe calibrated to give an EMME number for utilization with a nomogram ofFIG. 7. Those skilled in the art will realize that analogue-to-digitalconversion techniques can readily be incorporated to permit directcomputation for providing direct lean percentage reading.

For high volume applications, such as may be encountered with apermanent installation at a packing house, automation of the measureinitiating function is desirable and can readily be accomplished byutilizing a position sensor 43 which determines when the sample is inthe optimum measuring position at which time a measure initiatingcircuit 44 starts the measurement cycle in substantially the samefashion as with the manual initiating button 42.

While the principles of the invention have now been made clear in anillustrative embodiment, there will be immediately obvious to thoseskilled in the art many modifications of structure, arrangement,proportions, the elements, materials, and components, used in thepractice of the invention which are particularly adapted for specificenvironments and operating requirements without departing from thoseprinciples.

I claim:

1. The method of measuring the fat-to-lean ratio of animal tissuecomprising the steps of:

A. predetermining the effect of an animal tissue sample having knownfat-to-lean ratios on a standard electromagnetic field of knownintensity;

B. generating a test electromagnetic field of known intensity;

C. inserting a specimen of animal tissue having a fatto-lean ratio to bemeasured into the generated test electromagnetic field;

D. measuring the effect of the specimen on the generated testelectromagnetic field; and

E. correlating the measured effect of the specimen on the testelectromagnetic field to the predetermined effect.

2. The method of claim I in which the specimen of animal tissue to beanalyzed is weighed.

3. The method of claim 2 in which the dimensions of the specimen ofanimal tissue to be analyzed are determined.

4. The method of claim 1 in which the electromagnetic field is generatedby passing a time varying electric current through a conductor.

5. The method of claim 4 in which the effect of the specimen to beanalyzed in the electromagnetic field is measured indirectly bymeasuring the difference in impedance reflected by the conductor withoutand with the specimen disposed in the electromagnetic field.

6. The method of claim 5 in which the shape of the electromagnetic fieldis controlled by configuring the conductor generally solenoidally.

7. The method of claim 4 in which the temperature of the specimen ofanimal tissue to be analyzed is determined.

8. Apparatus for measuring the fat-to-lean ratio of animal tissuecomprising:

A. means for generating a time varying electromagnetic field comprising:

1. a waveform generator,

2. a coil, and

3. means coupling the output of said waveform generator to said coil;

B. feedback means for maintaining the time varying amplitude of saidelectromagnetic field constant, said feedback means including:

1. means for sensing and developing a field intensity signalproportional to the amplitude of said time varying electromagneticfield;

2. means for generating a standard signal representing a predeterminedelectromagnetic field amplitude;

3. comparator means for comparing said field intensity signal and saidstandard signal and for issuing a correction signal representative ofthe difference therebetween; and

4 variable gain means included in said coupling means, said variablegain means being responsive to said correction signal to alter the gainof said coupling means whereby the voltage and current applied to saidcoil maintain the amplitude of said electromagnetic field constant;

C. detector means for measuring the impedance reflected by said coil bysensing the voltage and current applied to said coil; and

D. means responsive to the difference in coil impedance with and withouta specimen of animal tissue to be graded to provide a quality signalcorresponding to said difference.

9. The apparatus of claim 8 in which said coil is solenoidally wound.

10. The apparatus of claim 9 in which said solenoidally wound coil iscompound wound with a plurality of coil segments and said means couplingsaid waveform generator to said coil is adapted to feed said coilsegments individually.

11. The apparatus of claim 9 in which said coil is surrounded by ashield to prevent factors outside said shield from affecting saidelectromagnetic field.

1. The method of measuring the fat-to-lean ratio of animal tissuecomprising the steps of: A. predetermining the effect of an animaltissue sample having known fat-to-lean ratios on a standardelectromagnetic field of kNown intensity; B. generating a testelectromagnetic field of known intensity; C. inserting a specimen ofanimal tissue having a fat-to-lean ratio to be measured into thegenerated test electromagnetic field; D. measuring the effect of thespecimen on the generated test electromagnetic field; and E. correlatingthe measured effect of the specimen on the test electromagnetic field tothe predetermined effect.
 2. The method of claim 1 in which the specimenof animal tissue to be analyzed is weighed.
 2. means for generating astandard signal representing a predetermined electromagnetic fieldamplitude;
 2. a coil, and
 3. means coupling the output of said waveformgenerator to said coil; B. feedback means for maintaining the timevarying amplitude of said electromagnetic field constant, said feedbackmeans including:
 3. comparator means for comparing said field intensitysignal and said standard signal and for issuing a correction signalrepresentative of the difference therebetween; and
 3. The method ofclaim 2 in which the dimensions of the specimen of animal tissue to beanalyzed are determined.
 4. The method of claim 1 in which theelectromagnetic field is generated by passing a time varying electriccurrent through a conductor.
 4. variable gain means included in saidcoupling means, said variable gain means being responsive to saidcorrection signal to alter the gain of said coupling means whereby thevoltage and current applied to said coil maintain the amplitude of saidelectromagnetic field constant; C. detector means for measuring theimpedance reflected by said coil by sensing the voltage and currentapplied to said coil; and D. means responsive to the difference in coilimpedance with and without a specimen of animal tissue to be graded toprovide a quality signal corresponding to said difference.
 5. The methodof claim 4 in which the effect of the specimen to be analyzed in theelectromagnetic field is measured indirectly by measuring the differencein impedance reflected by the conductor without and with the specimendisposed in the electromagnetic field.
 6. The method of claim 5 in whichthe shape of the electromagnetic field is controlled by configuring theconductor generally solenoidally.
 7. The method of claim 4 in which thetemperature of the specimen of animal tissue to be analyzed isdetermined.
 8. Apparatus for measuring the fat-to-lean ratio of animaltissue comprising: A. means for generating a time varyingelectromagnetic field comprising:
 9. The apparatus of claim 8 in whichsaid coil is solenoidally wound.
 10. The apparatus of claim 9 in whichsaid solenoidally wound coil is compound wound with a plurality of coilsegments and said means coupling said waveform generator to said coil isadapted to feed said coil segments individually.
 11. The apparatus ofclaim 9 in which said coil is surrounded by a shield to prevent factorsoutside said shield from affecting said electromagnetic field.